Comparison of ground‐ and satellite‐based measurements of the fraction of photosynthetically active radiation intercepted by tallgrass prairie

Concurrent measurements of the fraction of photosynthetically active radiation intercepted by vegetation canopies, F IPAR , and ground‐, helicopter‐, and satellite‐based reflectance measurements were taken at 13 tallgrass prairie sites. The sites were subjected to various combinations of burning and grazing managements. The ground‐ and helicopter‐based reflectance measurements were taken on the same day or within a few days of the time the Landsat and SPOT satellites passed over the sites. Sun photometer readings taken at the times of the satellite overpasses were used to correct for atmospheric attenuation. Hand‐held radiometer spectral indices were strongly correlated with the helicopter‐based values ( r = 0.94) and satellite‐based values ( r = 0.92 for Landsat thematic mapper (TM) and 0.86 for SPOT). However, the ground‐, the helicopter‐, and the satellite‐based normalized difference spectral vegetation indices showed low sensitivity to changes in F IPAR . Reflectance measurements were only moderately well correlated with measurements of F IPAR ( r = 0.82 for the hand‐held radiometer, 0.84 for helicopter measurements, 0.75 for SPOT, and 0.73 for the Landsat TM). Improved spectral indices that can compensate for site differences are needed to monitor F IPAR more reliably.